A higher than usual water bill is usually an indication of a leak. Most of the time the leak can not be seen or heard.
The first thing that should be done is to check the toilet by putting food coloring in the tank and letting the water sit for 30 minutes without flushing. If the water in the bowl turns color then there is a slow leak. If it doesn't seem to be the problem then perhaps a plumber should be called to check the pipes.
Once everything has been checked and there aren't any problems then contact the Town of Warrenton office at (540) 347-2678. The next step is for an employee to come out and check the water lines going to your house for any leaks.